Oftentimes, adaptive behavior relies on using memory for past events to guide upcoming decisions. To achieve this, memory structures in the brain interact with structures that exert cognitive control over the expression of such memories. This thesis investigated such interactions – the use of memory representations recently formed to guide adaptive behavior in the moment.
The medial temporal lobe (MTL) is critical for human memory. Its role in memory at long delays is well-established, while its contribution to memory at short delays had not been appreciated until recently, when studies specifically targeted the kind of processing it has come to be known for – binding of arbitrary relations among items in scenes or events into relational memory representations. In contrast, the role of the prefrontal cortex (PFC) in memory on this timescale has been well studied. One consequence of new insights about the role of MTL in memory under short delays is the question of how PFC fits into the picture. The framework for the work performed here is that the PFC exerts cognitive control over relational memory representations supported by the MTL.
The first experiment further shortened the delay, and investigated the role of the hippocampus in relational binding when there was no imposed delay. Using a restricted viewing paradigm, it was found that the hippocampus was critical for binding sequential glimpses into a coherent representation to guide exploration of a scene. The result demonstrated that, through its role in relational binding, the hippocampus contributes to task performance regardless of delays. The second experiment followed up on this finding, and investigated control processes carried out by the PFC that interact with MTL-based relational representations during ongoing behavior. Using fMRI, PFC-MTL interactions were studied using a search task that required frequent updates of cue-outcome relations. It was found that both the PFC and the hippocampus were involved during ongoing task performance but they displayed different activity profiles. Negatively correlated activity between the PFC and the hippocampus further suggested that the two regions were important for different aspects of the task. The third experiment focused on one type of cognitive control exerted by the PFC – interference resolution. In an fMRI experiment, it was found that the inferior frontal gyrus was active during interference resolution caused by recently studied object-location relations. Taken together, experiments in this thesis underscore the role of the hippocampus in relational binding, and demonstrate that the MTL and the PFC interact closely to guide adaptive behavior online.